1. Field of the Invention
The present invention is related to a method for making skeletal muscle semipermeable to pharmaceutical drugs, nucleic acids and other molecules. More specifically, skeletal muscle is made semipermeable by electrically stimulating the muscle with a current that generates low field strengths following injection of pharmaceutical drugs, nucleic acids and other molecules. The method can be used to obtain expression of proteins encoded by nucleic acids administered to muscle in accordance with the method.
2. Technical Background
Scientists are continually discovering genes which are responsible for many human diseases, such as genes responsible for some forms of breast cancer, colon cancer, muscular dystrophy and cystic fibrosis, In addition, scientists are continually discovering genes that code for bacterial and viral antigens (e.g., viral capsid proteins). Despite these new discoveries, a major obstacle facing the medical profession is how to safely deliver effective quantities of these agents to patients to treat disease or for genetic immunization.
Currently, most pharmaceutical agents are taken orally or intravenously. Oral and intravenous drug and gene delivery methods, however, have several shortcomings. First, a large percent of orally or intravenously delivered drugs are degraded by the body before arriving at the target organ or cells. Acids and enzymes in the stomach and intestine, for example, can break down many pharmaceutical drugs. Similarly, genes would be rapidly destroyed by proteins found in the blood and liver which break down DNA. Additionally, intravenously delivered drugs and genes are often sequestered by the liver or immune system before arriving at the diseased organ or cells. Second, oral and intravenous drug and gene delivery is non-specific. That is, the drug or gene is delivered to both target and non-target cells.
Skeletal muscle is a promising candidate for drug delivery, gene therapy and genetic immunization. First, skeletal muscle constitutes over 50% of a human's body mass, most of which is easily accessible compared to other tissues and organs of the body. Second, there are numerous inherited and acquired disorders, such as Duchenne muscular dystrophy (DMD), diabetes mellitus, hyperlipidaemia and cardiovascular disease which are good candidate disorders for drug and gene delivery into the muscle. Third, muscle is an ideal site for genetic immunization because it is easily accessible and proteins made in the muscle are secreted, thus eliciting an immune response. Finally, skeletal muscle cells are non-dividing. Therefore, skeletal muscle cells are capable of expressing a protein coded by a gene for a longer time period than would be expected of other cell types that are continually dividing. Because the protein is expressed for a longer time, fewer treatments would be necessary.
Currently, however, there is no non-viral method for effectively delivering pharmaceutical drugs, proteins, and DNA into skeletal muscle in vivo. There are several methods known in the art for transferring pharmaceutical drugs and DNA into skeletal muscle, such as intramuscular injection of DNA. The clinical applicability of direct muscle injection, however, is limited mainly because of low transfection efficiency, typically less than 1% transfection efficiency. It has been demonstrated that the efficacy of transfection can be improved if DNA injections are done in regenerating muscle. Regeneration is induced three days before DNA injection with the drug Bivucain. While injection in regenerating muscles induced by Bivucain show higher efficiency, the method has limited applicability in humans because of the severe damage caused to the muscle.
From the foregoing, it will be appreciated that it would be an advancement in the art to provide a non-viral method of delivering pharmaceutical drugs and DNA only to diseased organs and cells. It would also be an advancement in the art to provide an electroporation method of delivering pharmaceutical drugs and DNA directly into skeletal muscle. It would be yet another advancement in the art if the electroporation method could deliver therapeutically effective quantities of pharmaceutical drugs and DNA into the skeletal muscle at multiple sites simultaneously. It would be a further advancement if the method permitted the delivery efficiencies to be regulated.
Such a method is disclosed herein.